A pilot-operated three-port valve is known as disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2002-71033. This three-port valve includes three ports, two ring-shaped valve seats that are formed between these ports and that are concentric and opposite each other, a poppet-type valve member that is disposed between these two valve seats, and a pilot operating portion that opens and closes this valve member. This three-port valve is configured to open and close the valve member using a piston with a rod therebetween. The piston operates by the action of pilot fluid pressure of the pilot operating portion.
As described above, this type of three-port valve opens and closes two valve seats that are concentric and opposite each other using a single valve member therebetween. Therefore, in order to improve the sealing performance when either of the valve seats is closed, it is important that the ring-shaped seat surfaces of the two valve seats are parallel to each other and each seat surface and the corresponding seal surface of the valve member are parallel to each other.
However, in this type of three-port valve, due to a slight error during fabrication or assembly of components, the seat surfaces of the two valve seats are not always completely parallel to each other, and/or each seat surface and the corresponding seal surface of the valve member are not always completely parallel. In such a case, uneven contact between the valve member and the valve seats accelerates wear and tends to deteriorate sealing performance.